In Bhramha Purana, while describing about lord vishnu, it tells us why Lord Brahma born from the navel of Lord Vishnu
The Lord Vishnu bears a lotus on his navel, hence he is also known as Padmanabham.
Lord vishnu has removed Rajas from him through the navel by giving birth to Lotus. In that lotus the Lord Bhrahma Was born with holding the Vedas in one of his hand. Brahma has only royal virtues (Rajas or Rajoguna) and his work is to expand the universe for further creation. Thus Brahma is called ‘the creator’ and Vishnu the maintainer of the creation.
Well if any one is not interested in this creation or want to escape this creation Shiva, the destroyer helps in that process. Thus Shiva got the name ‘the Destroyer’.
Secret of lord Vishnu to acquire a peaceful form
Thus to remain in peaceful form Lord Vishnu has discarded all the royal virtues through his navel. Similarly he has made the sheshanaga (poisonous snake) which has darkness (Tamoguna or Tamas) as his seat. Thus only Satoguna (Virtue of the truth) remains with him. So Lord Vishnu acquired a peaceful form (Shantakaram).
One must first discard the virtues of royalty and darkness in one’s life to remain a peaceful form by not shattering in dark or poisonous times and not to indulge in royalties while one has it.